Prices aren't going down fast enough. You have to understand how this goes, beyond mere guesses. For 24GB of RAM (at least - and we're talking G5X or G6, not the cheaper DDR4 and upcoming DDR5 ) in any future console, in the amount of time you expect this (an unprecedented amount, for any console generation jump mind you - 16GB additional), that process would have had to start already. GPU manufacturers have also slowed development of their cards. That is one of the biggest factors. 

Of course i am mere guessing because no math can be used to determine future consoles ever, especially when this prediction is just for fun will not directly impact real PS5 development . Also we already have 16 GB HBM2 GPU from last year on Vega 64 with price around 500 to 600 USD. And also GPU manufacture is not slowing down it's just that AMD are focusing on mainstream and because of that Nvidia are becoming lazy.

You're looking at a 16GB G6 console at most. I can see Xbox being higher (thanks to the 4GB advantage the X has on the Pro), but the same mathematical logic applies. You're not going to suddenly get 28GB of RAM in the next system. We don't even have Game-ready GPUs on PC at that amount. The Titan Xp and V are the most powerful gaming cards around. How much RAM (both G5X and HBM 2 respectively)? 12GB. Next gen consoles have long been in production. Once that process began, RAM amount considerations were made, as devs always focus on that first. They know the market better than you or I and they know that, unless RAM prices see a significant (this is important) reduction in costs, then you will not be seeing a 24-28GB launch home console.

16 GB GDDR6 is possible if they are pushing PS5 to 2019 release date,  but if they able to hold until 2020 or 2021 that we might see more ram able to fit in, we also need to considered that consoles GPU pricing are different from desktop GPU.

Iterative consoles? That's another matter, but that will also depend on speed of reduction. Take it from a guy who happily buys lots of RAM. I'm sitting on 64GB of DDR4 because adding an additional 6$, as had planned to do in February, would have cost me $800. 32GB of RAM cost, on average, $360 right now. That would need to drop significantly (and soon) for what you want to occur.  

That's why my prediction can be different next year depend on how the price of ram goes. 

After people exaggerated the PS4-XB1 power differeantial to death, I doubt Xbox will let any other console be more powerful than it. Mark my words.

Console GPU pricing vs PC GPU pricing. Know all about it. That means little overall, though. For any of your predictions to come true, costs have to drop. No conflicting statements can change that.

Yeah I agree cost need to drop, but all of us here don't know abut the future, so it's just guessing. 

No, you don't need 24GB as a minimum. PC GPUs don't even need that (though such an amount would be wonderful). You'll get better output with more RAM, of course, but that much additional is not a necessity. 

The same thing happen with PS4 , who would have though that PS4 will be coming with 8 GB GDDR5, when their first prototype were using 4 GB GDDR5. At that time 4GB are even more then enough on PC. I remember at that time GTX 680 are using 2GB GDDR5.

A. If such a thing were to happen, MS would most likely go with an AMD CPU and an Nvidia GPU rather than give Sony a 2 year sales headstart on next gen or use an outdated Vega chip

That's why the keywords is "costume " , what the article trying to say is , Navi might be a customize SOC or a GPU that entirely based on customize SOC. Probably Microsot also have possibility on developing their own Navi. But for sure i would love to see Microsoft work again with Nvidia tho and the competition can become more interesting. 

B. Such a scenario would never happen anyway, MS has alot more money than Sony, Sony can't afford to pay AMD to make the entire Navi line PS exclusive, MS could easily outbid them. 

Microsoft money =/= Xbox Division Money , they can allocate their money solely to Xbox Division of course if they want and focusing on console , but such move will also depend on how the Xbox performed from early recent years and convince the board director and their investor to agree. SONY in terms of assets is not far from Microsoft and they are focusing more on PlayStation and they can and able to do that. 

My guess would be that only Navi 10 is exclusive to PS5, if it's even exclusive at all. MS will still have access to Navi 14 in 2020 I would assume. We know that MS doesn't just design one hardware prototype for a new console, they actually design multiple prototypes then finalize the prototype that best suits their price/performance needs in the year they plan to launch in.

I could see something like this for MS right now prototype wise:

Prototype #1 

Goal- 2019 release, in case Sony releases PS5 in 2019

CPU- 4-6 Zen Mobile cores, 8-12 threads (Zen mobile cores in use instead of Zen desktop cores to reduce CPU power usage as much as possible, to leave more room for GPU power usage)

GPU- Custom Vega 20 based GPU, which is cut down and underclocked to reduce power usage some, roughly 10-11 tflops, so a 70% increase in GPU power over XB1 X or more. 

RAM- 12 GB GDDR6

Hard drive- Probably 2 TB standard hard drive paired with 64GB of SSD cache to speed up load times

Price- Fluid. MS will be waiting to see how much PS5 is before they announce a price, then will undercut that price by $50-100, even if they have to sell at a loss to do it. Since this theoretical 2019 Xbox Scarlett would most likely be weaker than PS5 using Navi 10, MS will know they need to have the cheaper console if they want to be competitive.

Prototype #2

Goal- 2020 release, if Sony plans to release PS5 in 2020

CPU- 6-8 Zen mobile cores, 12-16 threads

GPU- Custom Navi 14 based GPU, cut down or underclocked to reduce power usage some, roughly 12-14 tflops. 

RAM- 16 GB GDDR6

Hard Drive- Probably 2 TB standard hard drive paired with 128GB of SSD cache to speed up load times

Price- Semi-fluid, but most likely $500